Summary: Alcoholic liver disease (ALD) is a health problem worldwide. Despite significant progresses made on the understanding of the pathogenesis and mechanisms, no effective treatment for ALD is available. Alcoholic steatosis is considered as the initial trigger of ALD and a critical causal factor for disease progression, as it sensitizes hepatocytes to oxidative stress and causes cellular damages that promote the pathogenesis of ALD. Clearly, identification of a novel pharmacological approach for preventing /reversing steatosis and for reducing hepatic oxidative stress in ALD, as well as understanding the underlying mechanisms, are urgently needed. Mitochondrion is the main organelle where lipids such as free fatty acid are oxidized. Mitochondrial uncoupling is a process that facilitates proton influx across mitochondrial inner membrane without generating ATP. As a result, mitochondrial uncoupling can increase lipid oxidation and reduce intracellular lipid accumulation. Mitochondrial uncoupling can be induced by mitochondrial uncoupler proteins (UCPs). Ectopically expressing UCP1 in mouse liver increases fatty acid oxidation, reduces lipid accumulation, and protects mice from high-fat diet-induced hepatic steatosis. Moreover, induction of UCP2 expression is a natural cellular response towards many types of cellular oxidative stress, as mitochondrial uncoupling effectively reduces the production of mitochondrial reactive oxygen species (ROS). These findings prompted us to hypothesize that induction of mitochondrial uncoupling in liver is an effective therapeutic strategy for treating alcoholic steatosis and reducing hepatic damage, thereby impacting on ALD progression. Mitochondrial uncoupling can be induced by chemical uncouplers. Niclosamide is an FDA approved anthelmintic drug and its mechanism of action is to induce mitochondrial uncoupling of parasitic worms. Our recent study (Nat. Med. 20: 1263-1269) demonstrated that oral niclosamide ethanolamine salt (NEN) is mainly distributed in mouse liver and oral NEN prevents and reverses hepatic steatosis and insulin resistance induced by a high-fat diet in mice. In a separate non-alcoholic steatohepatitis (NASH) mouse model, we showed that NEN can dramatically improve hepatic inflammation and fibrosis symptoms. Our long-term goal is to discover novel therapeutic strategies and develop effective therapeutics for ALD. The objective of this proposal is to evaluate the effectiveness of mitochondrial uncoupling on improving ALD symptoms and to investigate the underlying mechanisms. Two Specific Aims are proposed: 1. to examine the preventive and therapeutic effects of NEN- and UCP1- induced mitochondrial uncoupling on alcohol- induced steatosis and liver injury; 2. to determine the mechanisms by which mitochondrial uncoupling protects against alcohol-induced steatosis and liver injury. Positive outcomes will help validate a new therapeutic strategy and help develop new therapeutic options for the prevention and treatment of ALD.